Inside Health

OBSERVATORY

By Henry Fountain

Published: October 26, 2004

Slippery Hips

Artificial hips, knees and other joints have been a godsend for hundreds of thousands of people with severe arthritis and other degenerative bone diseases. But these ball and socket joints don't last forever.

The most serious problem affecting their longevity is bone loss caused by inflammation near the artificial joint. Simple wear and tear is involved: as the metal ball of the joint moves inside the polyethylene liner of the socket, tiny plastic particles are produced that cause an inflammatory response.

Now scientists in Japan have come up with a solution to reduce this bone loss. They've coated the inside of the polyethylene liner with a biocompatible polymer that greatly decreases friction and wear and tear. The polymer, known as MPC and developed by the same researchers, is currently used to coat stents and other medical devices to suppress biological reactions that can occur when a foreign object contacts living tissue.

The scientists grafted a coating of MPC on the polyethylene liner. They tested coated and uncoated joints, putting them through their paces in a mechanical hip-joint simulator.

As described in the journal Nature Materials, the researchers found that through about three million cycles of loading on the simulator, there was one-fourth as much wear on the MPC-coated joint as on the uncoated one. What's more, the wear particles that were produced in the coated joint were found to be biologically inert.

The researchers suggest that their technique will help improve artificial joints by reducing or eliminating the eventual loosening that occurs with bone loss.

Speeding Solar Wind

A speed record of sorts has been set in space. The solar wind, that thin flow of protons and other charged particles streaming from the Sun, has been clocked at speeds faster than 1,850 kilometers per second. That's more than 4.1 million miles per hour.

The speeds were observed in October and November of last year, following two large coronal mass ejections, events in which huge quantities of hot gas are expelled from the Sun's outer atmosphere. Ordinarily, the solar wind takes more than 48 hours to reach Earth, and its speed when it gets here is about 400 kilometers per second. In this case, travel time was probably on the order of 15 hours. By comparison, sunlight takes eight minutes to travel to Earth.

To calculate the speeds, scientists from Los Alamos National Laboratory, the Southwest Research Institute and other institutions analyzed data from a proton-monitoring instrument aboard the Advanced Composition Explorer spacecraft. The spacecraft, launched in 1997, orbits a point about a million miles from Earth where the Sun's and Earth's gravitational forces balance. The findings are being published in The Journal of Geophysical Research.

The scientists found that despite the high speeds, proton densities, dynamic pressure other aspects of the solar wind at the time were not unusual. At the time, the large coronal mass ejections created geomagnetic disturbances on Earth. But a larger solar storm occurred three weeks later, causing greater disturbance even though at 750 kilometers per second the solar wind speed was less than half the record-setting level.

Suffering Spruce

Last winter was a tough one in the Northeast. Tough on people, and, researchers at the University of Vermont say, tough on trees, too.

Brynne E. Lazarus, a graduate student, and colleagues studied red spruce trees in Vermont and surrounding states in early 2003 and found that foliage injury and death due to freezing was higher than in previous years dating back to 1986. Trees lost an average of 46 percent of their needles and 32 percent of the buds that had formed in 2002. The findings were reported in The Canadian Journal of Forest Research.

The researchers say they don't know precisely what caused the severe damage. The extremely cold weather last winter clearly had much to do with it, but pollution and other factors may have contributed. They say the damage can lead to further spruce decline and death in the following years.

An X-Y Mystery Solved

With its amalgam of mammalian, reptilian and avian features, the duck-billed platypus looks like one of the oddest beasts around. The view is just as strange in the cell nucleus. The platypus has 10 sex chromosomes instead of the normal 2.

The discovery, by Dr. Frank Gr?er of the Australian National University and colleagues, solves two longstanding mysteries about the platypus, which is found only in the wild in Australia.

When scientists study chromosomes in animals, they identify pairs, with one chromosome of paternal origin matched with a copy from the mother. ''But when people did that with the platypus, they'd always end up with chromosomes which they couldn't find a second copy for,'' Dr. Gr?er said.

What's more, he added, during meiosis, when cells divide to produce sperm or egg with only half the chromosomes, strange things happen, at least among the males. ''When people look at this stage in the male platypus, they see a number of chromosomes sticking together,'' he said, forming chains.

Dr. Gr?er thought there might be a link between the unpaired chromosomes and the chaining that occurs. So he and his colleagues used fluorescent labeling to track the chromosomes at various stages of cell division. The findings were reported in papers in the journal Nature and The Proceedings of the National Academy of Sciences.

In most mammals, including humans, one chromosome pair determines sex, and it is either XX (female) or XY (male). But in the platypus, the researchers found that out of 52 chromosomes, females had 10 X and males had 5 X and 5 Y.

This would seem to be a recipe for chaos when sperm and eggs are formed. Females would produce eggs with all X's, but formation of sperm cells would be like a dice game, with several ways to make 5 -- like 3X and 2Y, or 4Y and 1X.

Dr. Gr?er found that the platypus neatly avoids this problem, with a form of segregation. In the male, the 10 chromosomes don't pair up. They form a chain alternating X's and Y's . Then, when meiosis occurs, the X's and Y's separate. The X's stick together as do the Y's, forming chains of five, all X or all Y. When sperm and egg combine, the result can only be 10 X (female) or 5 X-5 Y (male).

The researchers also found more evidence of the platypus's strangeness: one X chromosome, the largest, is similar to human chromosomes, while another is more closely related to birds.